High density radio communications such as satellite broadcast systems, satellite communication systems, high-vision television broadcast systems, and cellular phone systems have come into wide use. And the frequency band in use is shifting to higher frequencies. To facilitate transportation of portable communication systems such as global positioning systems (navigation systems) and to make them smaller, miniaturization of the antenna for radio communication and the circuit substrate are desired.
An antenna for high frequency communication has a basic structure in which a metal foil such as copper foil is laminated on an antenna substrate. The antenna substrate is requested to be made from a material having a high dielectric constant and a low dielectric loss tangent. If the antenna substrate has these properties, even small antennae can receive and send high frequency radio waves. If the material has a high dielectric loss tangent, the transfer loss of information tends to be large and the sensitivity of receipt and transmission tends to have a low sensitivity and to be noisy. If the material has a low dielectric constant, the substrate or the antenna therefrom is difficult to be made small or to be miniaturized.
Formerly, some antenna substrates which have a high dielectric constant and a low dielectric loss tangent have been developed and are made of glass fibers prepregs, which have a comparatively high dielectric constant, preimpregnated with thermoset resins in which a powder of ceramics, which has a high dielectric constant, such as titania is added. However the process using such prepreg to make an antenna substrate is complicated and takes a great deal of time (i.e. &gt;24 hrs.).
On the other hand it is known that there are resins, such as polyphenyleneoxide and polyphenylene sulfide, which have a low dielectric loss tangent.
However, their dielectric constant is too low, and their electrical properties are affected by the environmental temperature. They cannot be used as a substrate for a small antenna or a small circuit.